Catalyst and process for making said catalyst

ABSTRACT

Disclosed is a zeolite base catalyst useful particularly for the selective production of para-dialkylsubstituted benzene. The catalyst comprises a porous crystalline zeolite having silica deposited thereon and having incorporated therein phosphorous. Described also in the process for making the catalyst and the parameters for the use of the catalyst in dialkylation processes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to particular modified zeolite catalysts andtheir uses in the selective production of para-dialkylsubstitutedbenzenes and to a process for converting certain charge stocks to a highyield of para-dialkylsubstituted benzenes.

Description of the Prior Art

U.S. Pat. No. 2,904,607 refers to the alkylation of aromatichydrocarbons with an olefin in the presence of a crystalline metallicaluminosilicate having uniform pore openings of about 6 to 15 Angstromunits. U.S. Pat. No. 3,251,897 describes alkylation of aromatichydrocarbons in the presence of X- or Y-type crystalline aluminosilicatezeolites, specifically such type zeolites wherein the cation is rareearth and/or hydrogen. U.S. Pat. Nos. 3,751,504 and 3,751,506 describesvapor phase alkylation of aromatic hydrocarbons with olefins, e.g.benzene with ethylene, in the presence of a ZSM-5 type zeolite catalyst.

More recently, U.S. Pat. No. 4,090,981 has disclosed a catalystparticularly applicable for the selective production ofpara-dialkylsubstituted benzenes. It comprises a porous crystallinealuminosilicate zeolite having silica deposited on the surface thereof.U.S. Pat. No. 4,127,616 is directed to the process utilizing thesezeolite compositions.

U.S. Pat. No. 3,962,364 describes the alkylation of aromatic compoundssuch as benzene and toluene with olefinic hydrocarbons, such asethylene, utilizing zeolites (ZSM-5, ZSM-11, ZSM-35, etc.) which havebeen reacted with phosphorous compounds.

SUMMARY OF THE INVENTION

In one aspect, this invention constitutes a catalyst compositioncomprising a porous crystalline zeolite having silica deposited thereon.The silica-treated zeolite further contains phosphorous. In anotheraspect this invention comprises a process for making the catalystcomposition of this invention comprising the steps of: impregnating azeolite material with a solution of a silicon compound, calcining theresultant product, further impregnating the calcined product with athermally decomposable phosphorous compound and subsequently calciningthis product. In still another aspect, this invention constitutes theprocess for making para-dialkylated aromatic compound comprisingreacting an olefinic compound and a substituted or unsubstitutedaromatic compound in the presence of the catalyst of this inventionunder suitable conditions to effect dialkylation.

DETAILED DESCRIPTION OF THE INVENTION

The zeolite base component of the present catalyst upon which silicadeposition is effected and in which phosphorous is incorporated ischaracterized by particular activity and sorption properties. Thus, theporous crystalline zeolite employed herein necessarily has: (1) anactivity, in terms of alpha value, of between 2 and about 5000, (2) axylene sorption capacity greater than 1 gram/100 grams of zeolite and(3) an ortho-xylene sorption time for 30 percent of said capacity ofgreater than 10 minutes, where the sorption capacity and sorption timeare measured at 120° C. (248° F.) and a xylene pressure of 4.5±0.8 mm ofmercury.

The alpha value reflects the relative activity of the catalyst withrespect to a silica-alumina cracking catalyst. To determine the alphavalue as such term is used herein, n-hexane conversion is determined atabout 538° C. (1000° F.). Conversion is varied by varying the spacevelocity such that a conversion level of 10 to 60 percent of n-hexane isobtained and converted to a rate constant per unit volume of zeolite andcompared with that of silica-alumina catalyst which is normalized to areference activity of 538° C. (1000° F.). Catalytic activity of thecatalysts is expressed as a multiple of this standard, i.e. thesilica-alumina standard. The silica-alumina reference catalyst containsabout 10 weight percent Al₂ O₃ with the remainder SiO₂. This method ofdetermining alpha, modified as described above, is more fully describedin the Journal of Catalysis, Vol. VI, Pages 278-287, 1966.

The measurements of hydrocarbon sorption capacities and rates areconveniently carried out gravimetrically on a thermal balance. Inparticular, it has been found that an equilibrium sorption capacity ofxylene, which can be either para, meta, ortho or a mixture thereof,preferably para-xylene since this isomer reaches equilibrium within theshortest time, of at least 1 gram per 100 grams of zeolite measured at120° C. and a xylene pressure of 4.5±0.8 mm of mercury and anortho-xylene sorption time for 30 percent of said capacity of greaterthan 10 minutes (at the same conditions of temperature and pressure) arerequired in order to achieve the desired selective production of paradialkyl substituted benzenes.

It has been found that zeolites exhibiting very high selectivity forpara-dialkylbenzene production require a very long time, up to andexceeding a thousand minutes, to sorb ortho-xylene in an amount of 30%of total xylene sorption capacity. For those materials it is moreconvenient to determine the sorption time for a lower extent ofsorption, such as 5%, 10%, or 20% of capacity, and to estimate the 30%sorption time applying the following multiplication factors F asillustrated for 5% sorption thus:

    ______________________________________                                                           Factor (F) to                                              t.sub.0.3 = (F) × (t.sub.0.05)                                                             Estimate 30%                                               Percent of sorption capacity                                                                     Sorption Time                                              ______________________________________                                         5                 36                                                         10                 9                                                          20                 2.2                                                        ______________________________________                                    

Zeolites such as zeolite X, zeolite Y, ZSM-4, faujasite, mordenite,ferrierite and offretite which satisfy the aforementioned activity andsorption characteristics are within the confines of this invention.Particularly preferred are zeolites having a silica to alumina ratio ofat least about 12 and a constraint index within the approximate range of1 to 12, such as ZSM-5, ZSM-11, ZSM-12, ZSM-35, ZSM-38. The zeolitesinduce profound transformation of aliphatic hydrocarbons to aromatichydrocarbons in commercially desirable yields and are generally highlyeffective in conversion reactions involving aromatic hydrocarbons.

Although these zeolites have unusually low alumina contents, i.e. highsilica to alumina mole ratios, they are very active even when the silicato alumina mole ratio exceeds 30. The activity is surprising sincecatalytic activity is generally attributed to framework aluminum atomsand/or cations associated with these aluminum atoms. These zeolitesretain their crystallinity for long periods in spite of the presence ofsteam at high temperature which induces irreversible collapse of theframework of other zeolites, e.g. of the X and A type. Furthermore,carbonaceous deposits, when formed, may be removed by burning at higherthan usual temperatures to restore activity. These zeolites, used ascatalysts, generally have low coke-forming activity and therefore areconducive to long times on stream between regenerations by burningcarbonaceous deposits with oxygen-containing gas such as air.

An important characteristic of the crystal structure of this novel classof zeolites is that it provides a selective constrained access to andegress from the intracrystalline free space by virtue of having aneffective pore size intermediate between the small pore Linde A and thelarge pore Linde X, i.e. the pore windows of the structure are of abouta size such as would be provided by 10-membered rings of silicon atomsinterconnected by oxygen atoms. It is to be understood, of course, thatthese rings are those formed by the regular disposition of thetetrahedra making up the anionic framework of the crystalline zeolite,the oxygen atoms themselves being bonded to the silicon (or aluminum,etc.) atoms at the centers of the tetrahedra.

The silica to alumina mole ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in the binder or in cationic or otherform within the channels. Although zeolites with a silica to aluminamole ratio of at least 12 are useful, it is preferred in some instancesto use zeolites having substantially higher silica/alumina ratios, e.g.1600 and above. In addition, zeolites as otherwise characterized hereinbut which are substantially free of aluminum, that is zeolites havingsilica to alumina mole ratios of up to infinity, are found to be usefuland even preferable in some instances. Such "high silica" or "highlysiliceous" zeolites are intended to be included within this description.Also to be included within this definition are substantially pure silicaanalogs of the useful zeolites described herein, that is to say thosezeolites having no measurable amount of aluminum (silica to alumina moleratio of infinity) but which otherwise embody the characteristicsdisclosed.

The novel class of zeolites, after activation, acquire anintracrystalline sorption capacity for normal hexane which is greaterthan that for water, i.e. they exhibit "hydrophobic" properties. Thishydrophobic character can be used to advantage in some applications.

The novel class of zeolites useful herein have an effective pore sizesuch as to freely sorb normal hexane. In addition, the structure mustprovide constrained access to larger molecules. It is sometimes possibleto judge from a known crystal structure whether such constrained accessexists. For example, if the only pore windows in a crystal are formed by8-membered rings of silicon and aluminum atoms, then access by moleculesof larger cross-section than normal hexane is excluded and the zeoliteis not of the desired type. Windows of 10-membered rings are preferred,although in some instances excessive puckering of the rings or poreblockage may render these zeolites ineffective.

Although 12-membered rings in theory would not offer sufficientconstraint to produce advantageous conversions, it is noted that thepuckered 12-ring structure of TMA offretite does show some constrainedaccess. Other 12-ring structures may exist which may be operative forother reasons and, therefore, it is not the present intention toentirely judge the usefulness of a particular zeolite solely fromtheoretical structure considerations.

Rather than attempt to judge from crystal structure whether or not azeolite possesses the necessary constrained access to molecules oflarger cross-section than normal paraffins, a simple determination ofthe "Constraint Index" as herein defined may be made by passingcontinuously a mixture of an equal weight of normal hexane and3-methylpentane over a sample of zeolite at atmospheric pressureaccording to the following procedure. A sample of the zeolite, in theform of pellets or extrudate, is crushed to a particle size about thatof coarse sand and mounted in a glass tube. Prior to testing, thezeolite is treated with a stream of air at 540° C. for at least 15minutes. The zeolite is then flushed with helium and the temperature isadjusted between 290° C. and 510° C. to give an overall conversion ofbetween 10% and 60%. The mixture of hydrocarbons is passed at 1 liquidhourly space velocity (i.e., 1 volume of liquid hydrocarbon per volumeof zeolite per hour) over the zeolite with a helium dilution to give ahelium to (total) hydrocarbon mole ratio of 4:1. After 20 minutes onstream, a sample of the effluent is taken and analyzed, mostconveniently by gas chromatography, to determine the fraction remainingunchanged for each of the two hydrocarbons.

While the above experimental procedure will enable one to achieve thedesired overall conversion of 10 to 60% for most zeolite samples andrepresents preferred conditions, it may occasionally be necessary to usesomewhat more severe conditions for samples of very low activity, suchas those having an exceptionally high silica to alumina mole ratio. Inthose instances, a temperature of up to about 540° C. and a liquidhourly space velocity of less than one, such as 0.1 or less, can beemployed in order to achieve a minimum total conversion of about 10%.##EQU1##

The Constraint Index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Zeolites suitable for the presentinvention are those having a Constraint Index of 1 to 12. ConstraintIndex (CI) values for some typical materials are:

    ______________________________________                                                          C.I.                                                        ______________________________________                                        ZSM-4               0.5                                                       ZSM-5               8.3                                                       ZSM-11              8.7                                                       ZSM-12              2                                                         ZSM-23              9.1                                                       ZSM-35              4.5                                                       ZSM-38              2                                                         ZSM-48              3.4                                                       TMA Offretite       3.7                                                       Clinoptilolite      3.4                                                       Beta                0.6                                                       H-Zeolon (mordenite)                                                                              0.4                                                       REY                 0.4                                                       Amorphous Silica-Alumina                                                                          0.6                                                       Erionite            38                                                        ______________________________________                                    

The above-described Constraint Index is an important and even criticaldefinition of those zeolites which are useful in the instant invention.The very nature of this parameter and the recited technique by which itis determined, however, admit of the possibility that a given zeolitecan be tested under somewhat different conditions and thereby exhibitdifferent Constraint Indices. Constraint Index seems to vary somewhatwith severity of operation (conversion) and the presence or absence ofbinders. Likewise, other variables such as crystal size of the zeolite,the presence of occluded contaminants, etc., may affect the constraintindex. Therefore, it will be appreciated that it may be possible to soselect test conditions as to establish more than one value in the rangeof 1 to 12 for the Constraint Index of a particular zeolite. Such azeolite exhibits the constrained access as herein defined and is to beregarded as having a Constraint Index in the range of 1 to 12. Alsocontemplated herein as having a Constraint Index in the range of 1 to 12and therefore within the scope of the defined novel class of highlysiliceous zeolites are those zeolites which, when tested under two ormore sets of conditions within the above-specified ranges of temperatureand conversion, produce a value of the Constraint Index slightly lessthan 1, e.g. 0.9, or somewhat greater than 12, e.g. 14 or 15, with atleast one other value within the range of 1 to 12. Thus, it should beunderstood that the Constraint Index value as used herein is aninclusive rather than an exclusive value. That is, a crystalline zeolitewhen identified by any combination of conditions within the testingdefinition set forth herein as having a Constraint Index in the range of1 to 12 is intended to be included in the instant novel zeolitedefinition whether or not the same identical zeolite, when tested underother of the defined conditions, may give a Constraint Index valueoutside of the range of 1 to 12.

The novel class of zeolites defined herein is exemplified by ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48 and other similarmaterials.

ZSM-5 is described in greater detail in U.S. Patents No. 3,702,886 andRe 29,948. The entire descriptions contained within those patents,particularly the X-ray diffraction pattern of therein disclosed ZSM-5,are incorporated herein by reference.

ZSM-11 is described in U.S. Pat. No. 3,709,979. That description, and inparticular the X-ray diffraction pattern of said ZSM-11, is incorporatedherein by reference.

ZSM-12 is described in U.S. Pat. No. 3,832,449. That description, and inparticular the X-ray diffraction pattern disclosed therein, isincorporated herein by reference.

ZSM-23 is described in U.S. Pat. No. 4,076,842. The entire contentthereof, particularly the specification of the X-ray diffraction patternof the disclosed zeolite, is incorporated herein by reference.

ZSM-35 is described in U.S. Pat. No. 4,016,245. The description of thatzeolite, and particularly the X-ray diffraction pattern thereof, isincorporated herein by reference.

ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859. Thedescription of that zeolite, and particularly the specified X-raydiffraction pattern thereof, is incorporated herein by reference.

ZSM-48 can be identified, in terms of moles of anhydrous oxides per 100moles of silica, as follows:

    (0-15)RN: (0-1.5)M.sub.2/n O: (0-2)Al.sub.2 O.sub.3 : (100)SiO.sub.2

wherein:

M is at least one cation having a valence n; and

RN is a C₁ -C₂₀ organic compound having at least one amine functionalgroup of pK_(a) >7.

It is recognized that, particularly when the composition containstetrahedral, framework aluminum, a fraction of the amine functionalgroups may be protonated. The doubly protonated form, in conventionalnotation, would be (RNH)₂ O and is equivalent in stoichiometry to 2RN+H₂O.

The characteristic X-ray diffraction pattern of the synthetic zeoliteZSM-48 has the following significant lines:

    ______________________________________                                        Characteristic Lines of ZSM-48                                                d (Angstroms) Relative Intensity                                              ______________________________________                                        11.9          W-S                                                             10.2          W                                                               7.2           W                                                               5.9           W                                                               4.2           VS                                                              3.9           VS                                                              3.6           W                                                               2.85          W                                                               ______________________________________                                    

These values were determined by standard techniques. The radiation wasthe K-alpha doublet of copper, and a scintillation counter spectrometerwith a strip chart pen recorder was used. The peak heights, I, and thepositions as a function of 2 times theta, where theta is the Braggangle, were read from the spectrometer chart. From these, the relativeintensities, 100 I/I_(o), where I_(o) is the intensity of the strongestline or peak, and d (obs.), the interplanar spacing in A, correspondingto the recorded lines, were calculated. In the foregoing table therelative intensities are given in terms of the symbols W=weak, VS=verystrong and W-S=weak-to-strong. Ion exchange of the sodium with cationsreveals substantially the same pattern with some minor shifts ininterplanar spacing and variation in relative intensity. Other minorvariations can occur depending on the silicon to aluminum ratio of theparticular sample, as well as if it has been subjected to thermaltreatment.

The ZSM-48 can be prepared from a reaction mixture containing a sourceof silica, water, RN, an alkali metal oxide (e.g. sodium) and optionallyalumina. The reaction mixture should have a composition, in terms ofmole ratios of oxides, falling within the following ranges:

    ______________________________________                                        REACTANTS    BROAD         PREFERRED                                          ______________________________________                                        Al.sub.2 O.sub.3 /SiO.sub.2                                                                =     0 to 0.02   0 to 0.01                                      Na/SiO.sub.2 =     0 to 2      0.1 to 1.0                                     RN/SiO.sub.2 =     0.01 to 2.0 0.05 to 1.0                                    OH.sup.- /SiO.sub.2                                                                        =     0 to 0.25   0 to 0.1                                       H.sub.2 O/SiO.sub.2                                                                        =     10 to 100   20 to 70                                       H.sup.+ (added)/SiO.sub.2                                                                  =     0 to 0.2    0 to 0.05                                      ______________________________________                                    

wherein RN is a C₁ -C₂₀ organic compound having amine functional groupof pK_(a) >7. The mixture is maintained at 80°-250° C. until crystals ofthe material are formed. H⁺ (added) is moles acid added in excess of themoles of hydroxide added. In calculating H⁺ (added) and OH values, theterm acid (H⁺) includes both hydronium ion, whether free or coordinated,and aluminum. Thus aluminum sulfate, for example, would be considered amixture of aluminum oxide, sulfuric acid, and water. An aminehydrochloride would be a mixture of amine and HCl. In preparing thehighly siliceous form of ZSM-48 no alumina is added. Thus, the onlyaluminum present occurs as an impurity in the reactants.

Preferably, crystallization is carried out under pressure in anautoclave or static bomb reactor at 80° C. to 250° C. Thereafter, thecrystals are separated from the liquid and recovered. The compositioncan be prepared utilizing materials which supply the appropriate oxide.Such compositions include sodium silicate, silica hydrosol, silica gel,silicic acid, RN, sodium hydroxide, sodium chloride, aluminum sulfate,sodium aluminate, aluminum oxide, or aluminum itself. RN is a C₁ -C₂₀organic compound containing at least one amine functional group ofpK_(a) >7, as defined above, and includes such compounds as C₃ -C₁₈primary, secondary, and tertiary amines, cyclic amine (such aspiperidine, pyrrolidine and piperazine), and polyamines such as NH₂-C_(n) H_(2n) -NH₂ wherein n is 4-12.

The original cations can be subsequently replaced, at least in part, bycalcination and/or ion exchange with another cation. Thus, the originalcations are exchanged into a hydrogen or hydrogen ion precursor form ora form in which the original cation has been replaced by a metal ofGroups I through VIII of the Periodic Table. Thus, for example, it iscontemplated to exchange the original cations with ammonium ions or withhydronium ions. Catalytically active forms of these would include, inparticular, hydrogen, rare earth metals, aluminum, manganese and othermetals of Groups I and VIII of the Periodic Table.

It is to be understood that by incorporating by reference the foregoingpatents to describe examples of specific members of the novel class withgreater particularity, it is intended that identification of the thereindisclosed crystalline zeolites be resolved on the basis of theirrespective X-ray diffraction patterns. As discussed above, the presentinvention contemplates utilization of such catalysts wherein the moleratio of silica to alumina is essentially unbounded. The incorporationof the identified patents should therefore not be construed as limitingthe disclosed crystalline zeolites to those having the specificsilica-alumina mole ratios discussed therein, it now being known thatsuch zeolites may be substantially aluminum-free and yet, having thesame crystal structure as the disclosed materials, may be useful or evenpreferred in some applications. It is the crystal structure, asidentified by the X-ray diffraction "fingerprint", which establishes theidentity of the specific crystalline zeolite material.

The specific zeolites described, when prepared in the presence oforganic cations, are substantially catalytically inactive, possiblybecause the intra-crystalline free space is occupied by organic cationsfrom the forming solution. They may be activated by heating in an inertatmosphere at 540° C. for one hour, for example, followed by baseexchange with ammonium salts followed by calcination at 540° C. in air.The presence of organic cations in the forming solution may not beabsolutely essential to the formation of this type zeolite; however, thepresence of these cations does appear to favor the formation of thisspecial class of zeolite. More generally, it is desirable to activatethis type catalyst by base exchange with ammonium salts followed bycalcination in air at about 540° C. for from about 15 minutes to about24 hours.

Natural zeolites may sometimes be converted to zeolite structures of theclass herein identified by various activation procedures and othertreatments such as base exchange, steaming, alumina extraction andcalcination, alone or in combinations. Natural minerals which may be sotreated include ferrierite, brewsterite, stilbite, dachiardite,epistilbite, heulandite, and clinoptilolite.

The preferred crystalline zeolites for utilization herein include ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, and ZSM-48, with ZSM-5 beingparticularly preferred.

In a preferred aspect of this invention, the zeolites hereof areselected as those providing among other things a crystal frameworkdensity, in the dry hydrogen form, of not less than about 1.6 grams percubic centimeter. It has been found that zeolites which satisfy allthree of the discussed criteria are most desired for several reasons.When hydrocarbon products or by-products are catalytically formed, forexample, such zeolites tend to maximize the production of gasolineboling range hydrocarbon products. Therefore, the preferred zeolitesuseful with respect to this invention are those having a ConstraintIndex as defined above of about 1 to about 12, a silica to alumina moleratio of at least about 12 and a dried crystal density of not less thanabout 1.6 grams per cubic centimeter. The dry density for knownstructures may be calculated from the number of silicon plus aluminumatoms per 1000 cubic Angstroms, as given, e.g., on Page 19 of thearticle ZEOLITE STRUCTURE by W. M. Meier. This paper, the entirecontents of which are incorporated herein by reference, is included inPROCEEDINGS OF THE CONFERENCE ON MOLECULAR SIEVES, (London, April 1967)published by the Society of Chemical Industry, London, 1968.

When the crystal structure is unknown, the crystal framework density maybe determined by classical pycnometer techniques. For example, it may bedetermined by immersing the dry hydrogen form of the zeolite in anorganic solvent which is not sorbed by the crystal. Or, the crystaldensity may be determined by mercury porosimetry, since mercury willfill the interstices between crystals but will not penetrate theintracrystalline free space.

It is possible that the unusual sustained activity and stability of thisspecial class of zeolites is associated with its high crystal anionicframework density of not less than about 1.6 grams per cubic centimeter.This high density must necessarily be associated with a relatively smallamount of free space within the crystal, which might be expected toresult in more stable structures. This free space, however, is importantas the locus of catalytic activity.

Crystal framework densities of some typical zeolites, including somewhich are not within the purview of this invention, are:

    ______________________________________                                                     Void     Framework                                                            Volume   Density                                                 ______________________________________                                        Ferrierite     0.28   cc/cc   1.76   g/cc                                     Mordenite      .28            1.7                                             ZSM-5, -11     .29            1.79                                            ZSM-12         --             1.8                                             ZSM-23         --             2.0                                             Dachiardite    .32            1.72                                            L              .32            1.61                                            Clinoptilolite .34            1.71                                            Laumontite     .34            1.77                                            ZSM-4 (Omega)  .38            1.65                                            Heulandite     .39            1.69                                            P              .41            1.57                                            Offretite      .40            1.55                                            Levynite       .40            1.54                                            Erionite       .35            1.51                                            Gmelinite      .44            1.46                                            Chabazite      .47            1.45                                            A              .5             1.3                                             Y              .48            1.27                                            ______________________________________                                    

When synthesized in the alkali metal form, the zeolite is convenientlyconverted to the hydrogen form, generally by intermediate formation ofthe ammonium form as a result of ammonium ion exchange and calcinationof the ammonium form to yield the hydrogen form. In addition to thehydrogen form, other forms of the zeolite wherein the original alkalimetal has been reduced to less than about 1.5 percent by weight may beused. Thus, the original alkali metal of the zeolite may be replaced byion exchange with other suitable metal cations of Groups I through VIIIof the Periodic Table, including, by way of example, nickel, copper,zinc, palladium, calcium or rare earth metals.

In accordance with this invention, a porous crystalline zeolite, asabove characterized, has silica deposited thereon and phosphorousincorporated therein. The silica is deposited on the zeolite bycontacting the latter with a silicone compound of a molecular sizeincapable of entering the pores of the zeolite and by subsequentlyheating in an oxygen-containing atmosphere, such as air, to atemperature above 300° C. but below a temperature at which thecrystallinity of the zeolite is adversely affected at a rate such thatthe silicone compound does not volatilize before undergoing oxidation tosilica.

The silicone compound utilized to effect the silica deposition ischaracterized by the general formula: ##STR1## where R₁ is hydrogen,fluorine, hydroxy, alkyl, aralkyl, alkaryl or fluoro-alkyl. Thehydrocarbon substituents generally contain from 1 to 10 carbon atoms andpreferably are methyl or ethyl groups. R₂ is selected from the samegroup as R₁, other than hydrogen and n is an integer of at least 10 andgenerally in the range of 10 to 1000. The molecular weight of thesilicone compound employed is generally between about 500 and about20,000 and preferably within the approximate range of 1000 to 10,000.Representative silicone compounds include dimethylsilicone,diethylsilicone, phenylmethylsilicone, methylhydrogensilicone,ethylhydrogensilicone, phenylhydrogensilicone, methylethylsilicone,phenylethylsilicone, diphenylsilicone, methyltrifluoropropylsilicone,ethyltrifluoropropylsilicone, polydimethylsilicone,tetrachlorophenylmethylsilicone, tetrachlorophenylethyl silicone,tetrachlorophenylhydrogen silicone, tetrachlorophenylphenyl silicone,methylvinylsilicone and ethylvinylsilicone.

The silicone compound dissolved in a suitable solvent therefor, e.g.,pentane, hexane, heptane, benzene, toluene, chloroform, carbontetrachloride, is contacted with the above described zeolite at atemperature between about 10° C. and about 100° C. for a period of timesufficient to deposit the ultimately desired amount of silicone thereon.Time of contact will generally be within the range of 0.2 to 5 hours,during which time the mixture is desirably subjected to evaporation. Theresulting residue is then calcined in an oxygen-containing atmosphere,preferably air, at a rate of 0.2° to 5° C./minute to a temperaturegreater than 200° C. but below a temperature at which the crystallinityof the zeolite is adversely affected. Generally, such temperature willbe below 600° C. Preferably the temperature of calcination is within theapproximate range of 350° to 550° C. The product is maintained at thecalcination temperature usually for 1 to 24 hour to yield a zeolitecomposition containing between about 0.5 and about 30 weight percent andpreferably between about 1 and 15 weight percent of silica.

The calcined product thus obtained is then contacted with a phosphorouscompound. Representative phosphorous-containing compounds includederivatives of groups represented by PX₃, RPX₂, R₂ PX, R₃ P, X₃ PO,(XO)₃ PO, (XO)₃ P, R₃ P=O, R₃ P=S, RPO₂, PPS₂, RP(O)(OX)₂, RP(S)(SX)₂,R₂ P(O)(OX), R₂ P(S)SX, RP(OX)₂, RP(Sx)₂ ROP(OX)₂, RSP(SX)₂, (RS)₂PSP(SR)₂, and (RO)₂ POP(OR)₂, where R is an alkyl or aryl, such asphenyl and X is hydrogen, R or halide. These compounds include primary,RPH₂, secondary, R₂ PH and tertiary, R₃ P, phosphines such as butylphosphine; the tertiary phosphine oxides R₃ PO, such astributylphosphine oxide, the tertiary phosphine sulfides, R₂ PS, theprimary RP(O)(OX)₂, and secondary, R₂ P(O)(OX), phosphonic acids such asbenzene phosphonic acid; the corresponding sulfur derivatives such asRP(S)(SX)₂ and R₂ P(S)SX, the esters of the phosphonic acids such asdiethyl phosphonate, (RO)₂ P(O)H, dialkyl alkyl phosphonates, (RO)₂P(O)R, and alkyl dialkylphosphinates, (RO)P(O)R₂ , phosphinous acids, R₂POX, such as diethylphosphinous acid, primary, (RO)P(OX)₂, secondary,(RO)₂ POX, and tertiary, (RO)₃ P, phosphites; and esters thereof such asthe monopropyl ester, alkyl dialkylphosphinites, (RO)PR₂, and dialkylalkyl phosphonites, (RO)₂ PR esters. Corresponding sulfur derivativesmay also be employed including (RS)₂ P(S)H, (RS)₂ P(S)R, (RS)P(S)R₂, R₂PSX, (RS)P(SX)₂, (RS)₂ PSX, (RS)₃ P, (RS)PR₂ and (RS)₂ PR. Examples ofphosphite esters include trimethylphosphite, triethylphosphite,diisopropylphosphite, butylphosphite; and pyrophosphites such astetraethylpyrophosphite. The alkyl groups in the mentioned compoundscontain 1 to 4 carbon atoms.

Other suitable phosphorous-containing compounds include the phosphorushalides such as phosphorus trichloride, bromide, and iodide, alkylphosphorodichloridites, (RO)PCl₂, dialkyl phosphorochloridites, (RO)₂PX, dialkylphosphinochloridites, R₂ PCl, alkylalkylphosphonochloridates, (RO)(R)P(O)Cl, dialkyl phosphinochloridates,R₂ P(O)Cl and RP(O)Cl₂. Applicable corresponding sulfur derivativesinclude (RS)PCl₂, (RS)₂ PX, (RS)(R)P(S)Cl and R₂ P(S)Cl.

Preferred phosphorous-containing compounds include monobasic and dibasicammonium phosphates diphenyl phosphine chloride, trimethylphosphite andphosphorus trichloride, phosphoric acid, phenyl phosphine oxychloride,trimethylphosphate, diphenyl phosphinous acid, diphenyl phosphinic acid,diethylchloro thiophosphate, methyl acid phosphate and other reactionproducts.

Reaction with the phosphorous compound of the product resulting fromdepositing silica on the zeolite and calcining it is effected bycontacting the calcined product with such compound. Where the treatingphosphorus compound is a liquid, such compound can be in solution in asolvent at the time contact with the zeolite is effected. Any solventrelatively inert with respect to the treating compound and the zeolitemay be employed. Suitable solvents include water and aliphatic, aromaticor alcoholic liquids. Where the phosphorus-containing compound is, forexample, trimethylphosphite or liquid phosphorus trichloride, ahydrocarbon solvent such as n-octane liquid phosphorus trichloride, ahydrocarbon solvent such as n-octane may be employed. Thephosphorus-containing compound may be used without a solvent, i.e., maybe used as a neat liquid. Where the phosphorus-containing compound is inthe gaseous phase, such as where gaseous phosphorus trichloride isemployed, the treating compound can be used by itself or can be used inadmixture with a gaseous diluent relatively inert to thephosphorus-containing compound and the zeolite-silica coated productsuch as air or nitrogen or with an organic solvent, such as octane ortoluene.

Heating of the phosphorus-containing silica-treated zeolite catalystsubsequent to preparation and prior to use is also preferred. Theheating can be carried out in the presence of oxygen, for example air.Heating can be at a temperature of about 150° C. However, highertemperatures, i.e., up to about 500° C., are preferred. Heating isgenerally carried out for 3-5 hours but may be extended to 24 hours orlonger. While heating temperatures above about 500° C. can be employed,they are not necessary. At temperatures of about 1000° C., the crystalstructure of the zeolite tends to deteriorate.

The amount of phosphorus incorporated with the zeolite should be atleast about 0.5 percent by weight. The amount of phosphorus can be ashigh as about 25 percent by weight or more depending on the amount andtype of binder present.

The amount of phosphorus incorporated with the silica-treated zeolite byreaction with the phosphorus-containing compound will depend uponseveral factors. One of these is the reaction time, i.e., the time thatthe zeolite and the phosphorus-containing source are maintained incontact with each other. With greater reaction times, all other factorsbeing equal, a greater amount of phosphorus is incorporated with thezeolite. Other factors upon which the amount of phosphorus incorporatedwith the zeolite is dependent include reaction temperature,concentration of the treating compound in the reaction mixture, thedegree to which the zeolite has been dried prior to reaction with thephosphorus-containing compound, the conditions of drying of the zeoliteafter reaction of the zeolite with the treating compound, and the amountand type of binder incorporated with the zeolite.

In practicing a particularly desired chemical conversion process, it maybe useful to incorporate the above-described crystalline zeolite with amatrix comprising another material resistant to the temperature andother conditions employed in the process. Such matrix material is usefulas a binder and imparts greater resistance to the catalyst for thesevere temperature, pressure and reactant feed stream velocityconditions encountered in many cracking processes.

Useful matrix materials include both synthetic and naturally occurringsubstances, as well as inorganic materials such as clay and/or metaloxides. The latter may be either naturally occurring or in the form ofgelatinous precipitates or gels including mixtures of silica and metaloxides. Naturally occurring clays which can be composited with thezeolite include those of the montmorillonite and kaolin families, whichfamilies include the sub-bentonites and the kaolins commonly known asDixie, McNamee-Georgia and Florida clays or others in which the mainmineral constituent is halloysite, kaolinite, dickite, nacrite oranauxite. Such clays can be used in the raw state as originally mined orinitially subjected to calcination, acid treatment or chemicalmodification.

In addition to the foregoing materials, the phosphorus-containingzeolites having a silica deposit thereon employed herein may becomposited with a porous matrix material, such as alumina,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The matrix may bein the form of a cogel. The relative proportions of zeolite componentand inorganic oxide gel matrix, on an anhydrous basis, may vary widelywith the zeolite content ranging from between about 1 to about 99percent by weight and more usually in the range of about 5 to about 80percent by weight of the dry composite.

The charge stock used herein for the selective production of paradialkyl substituted benzenes containing alkyl groups of 1 to 4 carbonatoms by contact, under conversion conditions, with the above-describedcatalyst includes a hydrocarbon precursor selected from the groupconsisting of mono alkylsubstituted benznes having 1-4 carbon atoms inthe alkyl-substituent, such as toluene, ethyl benzene, propyl benzene orbutyl benzene and a mixture of such precursor or benzene with analkylating agent containing from 1 to 4 carbon atoms.

Typical of the processes contemplated herein are disproportionation oftoluene to benzene and xylene, wherein the proportion of para-xyleneobtained is greatly in excess of its normal equilibrium concentration.Such process is effectively carried out at a temperature of betweenabout 400° C. and about 700° C. at a pressure between 1 and about 100atmospheres utilizing a weight hourly space velocity of between about 1and about 50.

The use of mixed aromatics as feed is also feasible. For example, amixture of ethylbenzene and toluene is converted selectively to amixture rich in p-diethylbenzene and p-ethyltoluene, the latterpredominating at high toluene to ethylbenzene ratios in the feed.

Reaction of benzene, toluene, ethylbenzene, propylbenzene orbutylbenzene with an alkylating agent containing from 1 to 4 carbonatoms is also contemplated using the catalyst described hereinabove.Suitable alkylating agents include olefins, alcohols, alkyl halides,ethers, sulfides having from 1 to 4 carbon atoms. Representative of suchcompounds are ethylene, propylene, butylene, methanol, ethanol,propanol, butanol, methyl chloride, ethyl chloride, propyl chloride,butyl chloride, dimethylether, dimethylsulfide, diethylether,diethylsulfide, dipropylether, dipropylsulfide, dibutylether anddibutylsulfide. Alkylation is suitably carried out at a temperaturebetween about 250° C. and about 700° C. at a pressure between about 1atmosphere and about 100 atmospheres employing a weight hourly spacevelocity of between about 0.1 and about 200.

It is contemplated that the conversion process described herein may becarried out as a batch type, semi-continuous or continuous operationutilizing a fixed or moving bed catalyst system. The catalyst after useis conducted to a regeneration zone wherein coke is burned from thecatalyst in an oxygen-containing atmosphere, e.g. air, at an elevatedtemperature, after which the regenerated catalyst is recycled to theconversion zone for further contact with the charge stock. With use ofthe present silica-coated zeolite catalyst, regeneration has been foundto restore the activity of the catalyst to a high level, therebyproviding a long catalyst life. It is particularly feasible to conductthe desired conversion in the presence of hydrogen utilizing ahydrogen-hydrocarbon mole ratio of between about 2 and about 20, withhydrogen pressure extending up to 100 atmospheres. The presence ofhydrogen in the reaction zone has been found to very substantiallyreduce the aging rate of the catalyst.

While the above process has been described with reference to selectiveproduction of para dimethyl substituted benzenes, typified bypara-xylene, it is contemplated that other para dialkyl substitutedbenzenes, wherein the alkyl group contains from 1 to 4 carbon atoms maysimilarly be selectively produced. Thus, utilizing the techniquedescribed herein, it is contemplated that with selection of a suitableprecursor, a mixture of ethyl benzene and toluene may be selectivelyconverted to para ethyl toluene; ethyl benzene may be selectivelyconverted to para diethyl benzene, propyl benzene may be converted todipropyl benzene and butyl benzene may be selectively converted todibutylbenzenes.

The following examples will serve to illustrate the process and catalystof the present invention without limiting the same.

EXAMPLE 1

To 0.51 grams of phenylmethylsilicone (molecular weight 1686) dissolvedin 20 cc of n-hexane was added 2.0 grams of NH₄ ZSM-5 having acrystallite size of approximately 0.5-4 microns. The mixture was thenevaporated using a rotary evaporator. The residue was heated in an oilbath for 1 hour at a temperature of 100° C. (212° F.) and was thencalcined in air at 1° C. per minute to 538° C. (1000° F.) and thenmaintained at this temperature for 7 hours.

Toluene, ethylene and hydrogen in a molar ratio of 8:1:3 respectivelywere passed over a portion of this catalyst at conditions of 385° C.(725° F.), 790 R Pa (100 psig), and WHSV of 29. After 4.3 hours of thistest had elapsed, analysis of the produced product showed a 96%consumption of ethylene. The concentration in the effluent ofpara-ethyltoluene was 88 mole percent and that of ortho-ethyltoluene0.33 mole percent. After 24.5 hours of the test, the ethyleneconsumption was 95% and the amounts of para-ethyltoluene andortho-ethyltoluene produced were 92% and 0.26% respectively.

EXAMPLE 2

To 21.4 grams of the catalyst prepared in Example 1 40 cc of 10%solution of diammonium phosphate was added and maintained in contact for2 hours. The solution was decanted from the catalyst material and theresulting catalyst product was then calcined in air at an increasingtemperature of 1° C. per minute until a temperature of 538° C. (1000°F.) was achieved. The catalyst was further calcined at a constanttemperature of 538° C. over a period of 7 hours.

This catalyst was then tested under conditions identical to those inExample 1. At the end of 2.2 hours analysis indicated the rate ofethylene consumption was 85% and the concentrations of para-ethyltolueneand ortho-ethyltoluene in the effluent product stream were 97% and 0.06%respectively. This latter test thus shows a substantial increase in theproduction of the desired para-ethyltoluene and a substantial decreasein the production of the undesired ortho-ethltoluene.

We claim:
 1. A catalyst composition comprising a porous crystallinezeolite, having silica deposited thereon as a result of contact with asilicone compound of a molecular size incapable of entering the pores ofthe zeolite and subsequent heating in an oxygen-containing atmosphere toa temperature in excess of 300° C. but below a temperature at whichcrystallinity of the zeolite is adversely affected at a rate such thatthe silicone compound does not volatilize prior to undergoing oxidationto silica, said zeolite being characterized by an activity, in terms ofalpha value, of between about 2 and about 5000, a xylene sorptioncapacity greater than 1 gram/100 grams of zeolite and an ortho xylenesorption time for 30 percent of said capacity greater than 10 minutes,said sorption capacity and sorption time being measured at 120° C. and apressure of 4.5±0.8 mm. of mercury and modified by the addition theretoof phosphorus.
 2. The catalyst composition of claim 1 wherein saidcrystalline zeolite has a silica to alumina ratio of at least about 12and a constraint index within the approximate range of 1 to
 12. 3. Thecatalyst composition of claim 1 wherein said crystalline zeolite isZSM-5.
 4. The catalyst composition of claim 3 wherein ZSM-5 ispredominately in the hydrogen form.
 5. The catalyst composition of claim1 wherein said crystalline zeolite is present in combination with abinder therefore.
 6. The catalyst composition of claim 1 wherein saiddeposited silica constitutes between about 0.5 and about 30 weightpercent of the composition.
 7. The catalyst of claim 1 wherein theamount of phosphorus is at least 0.5 percent by weight of the porouscrystalline zeolite.
 8. The catalyst of claim 1 wherein the phosphorusaddition is accomplished by contacting the porous crystalline zeolitehaving silica deposited thereon with a phosphorus compound.
 9. Thecatalyst of claim 8 wherein said phosphorus compound is monobasicammonium phosphate.
 10. The catalyst of claim 8 wherein said phosphorouscompound is dibasic ammonium phosphate.
 11. The catalyst of claim 8wherein said phosphorus compound is phosphorus acid.
 12. The catalyst ofclaim 8 wherein said phosphorous compound is methyl acid phosphate. 13.The catalyst of claim 8 wherein said phosphorus compound is a P₂ O-₅alcohol reaction product.
 14. The catalyst of claim 8 wherein saidphosphorus is present in an amount of between about 0.5 and about 25weight percent.
 15. A method for making the catalyst composition ofclaim 1 comprising:(a) depositing silica on said zeolite by contactingsaid zeolite with a silicone compound of a molecular size incapable ofentering the pores of the zeolite, said silicone compound having thegeneral formula: ##STR2## where R₁ is hydrogen, fluorine, hydroxy,alkyl, aralkyl, alkaryl, or fluoro-alkyl, the hydrocarbon substitutentscontaining from 1 to 10 carbon atoms, R₂ is selected from the same groupas R₁, other than hydrogen and n is an integer of at least 10; and (b)contacting the resultant residue with a phosphorus compound.
 16. Themethod of claim 15 wherein subsequent to step (a) and prior to step (b)the resultant residue is heated in an oxygen containing atmosphere to atemperature in excess of 200° C. but below a temperature at which thecrystallinity of the zeolite is adversely affected at a rate such thatthe silicone compound is not volatilized before undergoing oxidation tosilica.
 17. The method of claim 16 wherein subsequent to contacting saidresidue with a phosphorous compound the resulting product is heated at atemperature up to about 500° C.
 18. The method of claim 16 wherein saidheating takes place at a rate of 0.2° to 5° C./minute.
 19. The method ofclaim 15 wherein said zeolite has a silica to alumina ratio of at leastabout 11 and a constraint index within the approximate range of 1 to 12.20. The method of claim 15 wherein said zeolite is ZSM-5.
 21. The methodof claim 15 wherein said silicone is selected from the group consistingof dimethylsilicone, diethylsilicone, phenylmethylsilicone,methylhydrogensilicone, ethylhydrogensilicon phenylhydrogensilicone,methylethylsilicone, phenylethylsilicone, diphenylsilicone,methyltrifluoropropylsilicone, ethyltrifluoropropylsilicone,polydimethylsilicone, tetrachlorophenylmethyl silicone,tetrachlorophenylethyl silicone, tetrachlorophenylhydrogen silicone,tetrachlorophenylphenyl silicone, methylvinylsilicone andethylvinylsilicone.
 22. The method of claim 15 wherein said phosphoruscompound is selected from the group consisting of phosphoric acid. 23.The method of claim 15 wherein said phosphorus compound is diammoniumphosphate.
 24. The method of claim 15 wherein said phosphorus compoundis methyl acid phosphate.
 25. The method of claim 15 wherein saidphosphorus compound is a P₂ O₅ -alcohol reaction product.